#!/usr/bin/env python3

import random

def main():
    trials = 1000000
    sets = []
    for i in range(trials):
        a = 0   # first (eldest) child is always a girl
        b = random.randrange(2)   # parents have second child (coinflip)
        sets.append((a, b))

    num_boys = 0  # number of times the edlest's sibling is a boy
    num_girls = 0 # number of times the edlest's sibling is a girl
    for s in sets:
        if s[1] == 1:  # sibling is a boy
            num_boys += 1
        else:
            num_girls += 1

    print ("Number of times sibling is a boy: %d" % num_boys)
    print ("Number of times sibling is a girl: %d" % num_girls)
    print ("Probability of sibling being a boy: %.2f%%" % (num_boys / (num_boys + num_girls) * 100))

if __name__ == '__main__':
    main()